400E 1992 400E misfiring after installing engine harness

[Gbowman]

Hey everyone! I'm new to the 500e board. Been trying to get some answers on some W124 Facebook groups and was referred to the 500eboard.
I recently bought a 1992 400e with intentions of fixing it up and I fear I may have gone in over my head. When I bought it it had the ASR and ABS light on and it ran okayish, but smelled a bit rich. I did the blink test and have about 16 codes, and the ones relating to the fuel injection module won't clear. Those being:

8 Camshaft position sensor signal. Open or short circuit.
13 Intake air temperature sensor, open or short circuit.
25 Adjustable camshaft timing solenoid, open or short circuit

I have already replaced the upper engine wiring harness as it was very deteriorated and it went from running somewhat decent to misfiring at random. As it sits it will not pass emmisions.

Also the water temp gauge on the dash randomly shoots up to max temperature. I don't know if that has something to do with it.

 

[jhodg5ck]

hate to ask the basics, but what shape is the ignition system in? Did you go through caps/rotors/insulators/plugs? Wires will tolerate a lot of abuse but you can test them/ohm them out and see if they're good.

If you pull the harness that feeds your cam magnets you can put 12 v to it at idle and your idle should visibly degrade, but that might be hard to discern if it's running like crap.

Temp gauge is it's own gig, so not likely. I would change/clean all your fuses/relays and modules in the box. Also check your 38 pin diagnostic connector for degradation. That'll make Strange things happen when it starts to break down.

jono

 

[gsxr]

Hey everyone! I'm new to the 500e board. Been trying to get some answers on some W124 Facebook groups and was referred to the 500eboard.
I recently bought a 1992 400e with intentions of fixing it up and I fear I may have gone in over my head. When I bought it it had the ASR and ABS light on...

The ABS/ASR lights on are only for braking and traction control systems, and have nothing to do with the engine management (running rich, misfiring, power loss, etc). Have you checked fault codes for ABS/ASR (diagnostic socket #6) and throttle control (E-GAS, socket #7)? This needs to be diagnosed separately from the engine issues. Check the date code on the ETA (throttle body), if original, it likely needs a rebuild even though the wires may be fine. There will usually be fault codes on the E-GAS but not always.

and it ran okayish, but smelled a bit rich. I did the blink test and have about 16 codes, and the ones relating to the fuel injection module won't clear. Those being:

8 Camshaft position sensor signal. Open or short circuit.
13 Intake air temperature sensor, open or short circuit.
25 Adjustable camshaft timing solenoid, open or short circuit

#8 and #25 could be related to the engine harness, but after installing the new harness, these should go away. However, you need to manually clear each code with the blink code reader. #13 should also be investigated, but will have little effect on engine operation, so that's low priority.

I have already replaced the upper engine wiring harness as it was very deteriorated and it went from running somewhat decent to misfiring at random.

The misfiring is likely a separate issue, not related to the engine harness. You'll nee to remove the caps, rotors, rotor bracket, and insulator for inspection. If the caps/rotors are in poor condition, and/or there is liquid on the back of the insulator, they may need replacement. You'll also need to eliminate oil leaks from the cam sprocket seal behind the insulator, and from the cam solenoids. And add vent slots to the caps. More info in this thread.

As it sits it will not pass emmisions.

What is the failure mode? Idle, 2500rpm, CO, HC, etc? Can you post the emission test results?

Also the water temp gauge on the dash randomly shoots up to max temperature. I don't know if that has something to do with it.

The dash temp gauge is not connected to any engine management computers. However, this is routed through the upper engine harness. Did you install a brand new harness from the dealer, or did you buy a used one? It's possible, but unlikely, that your gauge is bad... more likely something is still fishy with the upper engine harness. The coolant temp sensors are all at the front of the intake manifold, the 1-pin is for the dash gauge, 2-pin is for HVAC and twin electric fans, 4-pin is for the engine computers.

BTW - welcome to the forum!

 

[Gbowman]

The ABS/ASR lights on are only for braking and traction control systems, and have nothing to do with the engine management (running rich, misfiring, power loss, etc). Have you checked fault codes for ABS/ASR (diagnostic socket #6) and throttle control (E-GAS, socket #7)? This needs to be diagnosed separately from the engine issues. Check the date code on the ETA (throttle body), if original, it likely needs a rebuild even though the wires may be fine. There will usually be fault codes on the E-GAS but not always.



#8 and #25 could be related to the engine harness, but after installing the new harness, these should go away. However, you need to manually clear each code with the blink code reader. #13 should also be investigated, but will have little effect on engine operation, so that's low priority.




The misfiring is likely a separate issue, not related to the engine harness. You'll nee to remove the caps, rotors, rotor bracket, and insulator for inspection. If the caps/rotors are in poor condition, and/or there is liquid on the back of the insulator, they may need replacement. You'll also need to eliminate oil leaks from the cam sprocket seal behind the insulator, and from the cam solenoids. And add vent slots to the caps. More info in this thread.



What is the failure mode? Idle, 2500rpm, CO, HC, etc? Can you post the emission test results?




The dash temp gauge is not connected to any engine management computers. However, this is routed through the upper engine harness. Did you install a brand new harness from the dealer, or did you buy a used one? It's possible, but unlikely, that your gauge is bad... more likely something is still fishy with the upper engine harness. The coolant temp sensors are all at the front of the intake manifold, the 1-pin is for the dash gauge, 2-pin is for HVAC and twin electric fans, 4-pin is for the engine computers.

BTW - welcome to the forum!

Thanks for all the info! The E test failed with HC being 2.8 ppm with a limit of 1.2 and the NOx being 4.3 ppm with a limit of 3 ppm. I have attached the graph that the emmisions place gave me.

The previous owner said he put in all new distributers and plug wires and they look pretty new but I have yet to take the caps off and check.

I did check the codes in all of the different modules. I did not actually clear them correctly though it seems. I'll have to try and clear them again tonight and see what comes back. The codes are as follows-

abs

9 Right rear axle solenoid valve

efi

8 Camshaft position sensor signal. Open or short circuit.
13 Intake air temperature sensor, open or short circuit.
25 Adjustable camshaft timing solenoid, open or short circuit

EA/CC/ISC

3 Right EA/CC/ISC actuator (left cylinder bank) (M16/1)
2 EA/CC/ISC control module (N4/1) or
Safety contact switch (M16/1s1) or
Stop lamp switch or
Cruise control switch or
Actual value potentiometer or
Starter lock-out/back-up lamp switch or
Engine speed signal or
Vehicle speed signal or
Closed throttle position switch or
Safety relay in EA/CC/ISC control module
11 Closed throttle recognition signal to engine control module (HFM-SFI or Left LH-SFI)
Fuel safety shut-off to engine control module (HFM-SFI or left or right LH-SFI)

BM

6 Electromagnetic a/c compressor clutch blocked
9 Voltage supply for LH-SFI control module interrupted
10 Voltage supply for LH-SFI control module interrupte, Voltage supply for fuel injectors interrupted
11 Voltage supply for accessory equipment control module interrupted
12 Voltage supply for ABS control module, ABS/ASR control module or ASD control module interrupted
17 Voltage supply for module box blower motor interrupted

DI control mod
6 Camshaft position sensor faulty

Airbag/SRS

3 Driver Airbag squib (Firing charge circuit)
8 Voltage supply interrupted (Circuit 15R)

 

[gsxr]

Thanks for all the info! The E test failed with HC being 2.8 ppm with a limit of 1.2 and the NOx being 4.3 ppm with a limit of 3 ppm. I have attached the graph that the emmisions place gave me.

I'm not familiar with emissions measured as GPM (Grams per Mile). Typically HC is PPM (parts per million) and CO/NO2 is a percentage. How are they testing this at speed, since the graph shows MPH? With ASR, you can't run the car on a chassis dyno for emission testing. Is the shop performing the test properly?

Separately, the catalyst must be FULLY HOT to get decent HC measurements. Simply heating the cats properly can make a huge difference in HC readings. More info here.

The previous owner said he put in all new distributers and plug wires and they look pretty new but I have yet to take the caps off and check.

Yeah, remove EVERYTHING and inspect. Nobody replaces the insulators or removes them to check the back side. Also verify the spark plugs are proper NON-resistor F8DC4 or equivalent, ideally gapped at 1.0mm (not 0.8mm). If it has resistor plugs, replace them with the correct plugs. The insulator should be tan, if it's coal black, something is wrong with the mixture.

If the caps look good visually, add the ventilation slots as shown in the thread linked earlier. Is the misfiring constant, from a cold start through warmup? Or is it only when cold, only when hot, only under load, etc?

I did check the codes in all of the different modules. I did not actually clear them correctly though it seems. I'll have to try and clear them again tonight and see what comes back. The codes are as follows-

Yep - that is "code diarrhea". Clear everything and drive the car for a couple days, then see which codes (if any) return.


Also, check what LH module is installed. It needs to be correct for the 1992 400E. If it is, next step is to open it up and verify nobody installed a "performance" EPROM chip, which could cause problems with emissions. Finally, make sure the fuel pump relay located below the rear seat bench is not clicking at idle - if so, the capacitors inside the LH module need replacement.

 

[Gbowman]

I'm not familiar with emissions measured as GPM (Grams per Mile). Typically HC is PPM (parts per million) and CO/NO2 is a percentage. How are they testing this at speed, since the graph shows MPH? With ASR, you can't run the car on a chassis dyno for emission testing. Is the shop performing the test properly?

Separately, the catalyst must be FULLY HOT to get decent HC measurements. Simply heating the cats properly can make a huge difference in HC readings. More info here.




Yeah, remove EVERYTHING and inspect. Nobody replaces the insulators or removes them to check the back side. Also verify the spark plugs are proper NON-resistor F8DC4 or equivalent, ideally gapped at 1.0mm (not 0.8mm). If it has resistor plugs, replace them with the correct plugs. The insulator should be tan, if it's coal black, something is wrong with the mixture.

If the caps look good visually, add the ventilation slots as shown in the thread linked earlier. Is the misfiring constant, from a cold start through warmup? Or is it only when cold, only when hot, only under load, etc?



Yep - that is "code diarrhea". Clear everything and drive the car for a couple days, then see which codes (if any) return.


Also, check what LH module is installed. It needs to be correct for the 1992 400E. If it is, next step is to open it up and verify nobody installed a "performance" EPROM chip, which could cause problems with emissions. Finally, make sure the fuel pump relay located below the rear seat bench is not clicking at idle - if so, the capacitors inside the LH module need replacement.

They did put in on a Dyno for the emmisions, but it was an awd dyno that spins all 4 tires at the same speed.

I'll tear apart the ignition system tonight and let you know what I see. Do you know what tools I'll need for the job? I work as a diesel mechanic and have all of my tools at the shop I work in and will need to bring them home.

I haven't driven it very much since I replaced the engine wiring harness. Maybe 10 minutes to test it, but it seemed to run fine for a few and then when I stopped in my driveway it felt like it was running on 4 cylinders. I fired it up again to move it at a later date and it missed for only about 30 seconds to a minute then cleared up again. And when I went to pull it in to my garage yesterday to get the codes it was running fine.

 

[gsxr]

They did put in on a Dyno for the emmisions, but it was an awd dyno that spins all 4 tires at the same speed.

Dang, they are hard core. California just lets these cars do a stationary test!

I'll tear apart the ignition system tonight and let you know what I see. Do you know what tools I'll need for the job? I work as a diesel mechanic and have all of my tools at the shop I work in and will need to bring them home.

Mostly just metric Allen wrenches. Be careful with the rotor bolts, which are 3mm hex socket... if the rotors are Bosch, the bolts have a funky size like 3.27mm or something where no metric nor SAE fits well. DO NOT use ball-end tools to break these loose, you risk stripping them, and creating a bigger problem. I think the caps are either 4mm or 5mm hex socket.

I haven't driven it very much since I replaced the engine wiring harness. Maybe 10 minutes to test it, but it seemed to run fine for a few and then when I stopped in my driveway it felt like it was running on 4 cylinders. I fired it up again to move it at a later date and it missed for only about 30 seconds to a minute then cleared up again. And when I went to pull it in to my garage yesterday to get the codes it was running fine.

There's a scenario where the engine will cold start and run smoothly, then after 5-10 minutes of driving, it starts to misfire badly. It will often clear up after another 10-20 mins of driving (not recommended, as raw fuel can get dumped into the cats, with high risk of fire) or if the car sits for 30-60 mins... then it runs flawlessly, until the next cold start (sometimes needs to be parked for days or weeks before it recurs). If this is what's going on, it's definitely secondary ignition, and the fix is in that thread linked back in post #3 above (add cap vent slots, check all components, fix all oil leaks in that area).

 

[Gbowman]

Dang, they are hard core. California just lets these cars do a stationary test!




Mostly just metric Allen wrenches. Be careful with the rotor bolts, which are 3mm hex socket... if the rotors are Bosch, the bolts have a funky size like 3.27mm or something where no metric nor SAE fits well. DO NOT use ball-end tools to break these loose, you risk stripping them, and creating a bigger problem. I think the caps are either 4mm or 5mm hex socket.




There's a scenario where the engine will cold start and run smoothly, then after 5-10 minutes of driving, it starts to misfire badly. It will often clear up after another 10-20 mins of driving (not recommended, as raw fuel can get dumped into the cats, with high risk of fire) or if the car sits for 30-60 mins... then it runs flawlessly, until the next cold start (sometimes needs to be parked for days or weeks before it recurs). If this is what's going on, it's definitely secondary ignition, and the fix is in that thread linked back in post #3 above (add cap vent slots, check all components, fix all oil leaks in that area).

Just tore everything apart.

Plug wires look great.

Spark plugs look decent if not a little rich, a few of them had some wet fuel on them. Couldn't find my spark plug gap tool so couldn't get the gap but they are definitely Mercedes OEM. I'll probably go ahead and replace them anyways while I got it apart.

Distributers look a bit worn. They might clean up and be fine, but it might be worth replacing them anyway. The drivers distributor has some oil residue around the cap, but it looks bone dry inside the cap itself.

I took out the LH module and it looks like it's never been apart and it has the date code of 01/92, so it looks original.

Also noticed that the ETA was acting somewhat weird when I was trying to scan codes yesterday. I have a video but it's too large to attach to the thread. With KOEO it makes a high pitched noise. If you open the throttle to about halfway it clicks and stops making the noise then goes back to all the way closed, but if you let off the throttle then go back on to the throttle it opens back up again but only to about 60-70%

 

[Alphasud40]

Yea the front range of Colorado has one of the toughest emissions test requirements. Manufacturers send their cars to Denver for emissions compliance in high altitude conditions. I went through the state run emissions class. The instructor was brilliant and one of the best classes I ever participated in. NOX is going to be hard to pass and most likely you might end up replacing the cats. NOX is a byproduct of high combustion temperatures. A high compression engine running at stoichiometric generates a lot of NOX. That’s what the 3-way catalyst was designed to cope with. Rich running engines will be low on NOX so to be high in both HC and NOX is generally a tired catalyst. Try cheating by adding a few gallons of e85 to a 3/4 tank and run the car hard. Hopefully that will make it pass. As for the rough running as suggested replace the caps and rotors and don’t forget the insulators.

 

[gsxr]

Also noticed that the ETA was acting somewhat weird when I was trying to scan codes yesterday. I have a video but it's too large to attach to the thread. With KOEO it makes a high pitched noise. If you open the throttle to about halfway it clicks and stops making the noise then goes back to all the way closed, but if you let off the throttle then go back on to the throttle it opens back up again but only to about 60-70%

This is normal. With KOEOthe ETA (which is fully drive-by-wire, with mechanical backlup) does a "startup dance" complete with whining, clicking, and some butterfly movement. When they are silent, that's bad.

You should not manually move the linkage behind the airbox with KOEO, this will trigger fault codes and put the system into limp mode, where the butterfly only operates mechanically. If done with engine running, you'll get ABS+ASR lights on. Shutting the ignition off and restarting will clear limp mode (and warning lamps) but the codes must be manually cleared. To view throttle operation you need a second person to press the accelerator pedal while you view butterfly movement.

 

[natejgreene9871]

My vote is you probably have biodegradable wiring in the ETA harness. If upper harness was original I’m sure the eta is as well. Carefully slit the cable open and see.

I think you will be chasing your tail until you confirm this.

Once the bio wiring is rectified, I would clear all the codes and replace your caps and rotors. See what codes come back

 

[Gbowman]

This is normal. With KOEOthe ETA (which is fully drive-by-wire, with mechanical backlup) does a "startup dance" complete with whining, clicking, and some butterfly movement. When they are silent, that's bad.

You should not manually move the linkage behind the airbox with KOEO, this will trigger fault codes and put the system into limp mode, where the butterfly only operates mechanically. If done with engine running, you'll get ABS+ASR lights on. Shutting the ignition off and restarting will clear limp mode (and warning lamps) but the codes must be manually cleared. To view throttle operation you need a second person to press the accelerator pedal while you view butterfly movement.

Hey so I have been working the ol Benz here and there. Got all new spark plugs in it, was going to replace the cap and rotors but my eyes started watering when I saw the price on them. Decided to just clean my old ones up and throw it back together. Cleared all the codes and took it for a little 2-3 mile test drive. Not getting any engine codes returning and it seems like the misfire is no longer present.

Although it still seems like it's running rich and it's spitting out some real stinky fumes. I still don't think it will pass an Etest

 

[gsxr]

Although it still seems like it's running rich and it's spitting out some real stinky fumes. I still don't think it will pass an Etest

Read the end of post #5 above. Also, go for a longer test drive... 3 miles isn't getting anything near operating temp. 30 minutes would be a good exercise.

 

[emerydc8]

My experience has been 100% in line with @gsxr's post #5. The old catylitic converters don't really do a good job until really warmed up (probably the reason for the air pump). In order to get mine through emissions I drive it to the testing facility in second gear and 4000 RPM for a few miles prior and if I'm waiting in line I'll also bring the RPM up to 3000 for a few minutes just before my turn (just keep an eye on the coolant temp).

I don't know what state you're in but here in Arizona the 500E/400E from 1992-1995 is exempt from doing the dynamic roller test due to the ASR. Since you have ASR you should be exempt. Sometimes I have to request a supervisor to convince the testers. If push comes to shove I tell them that the roller test has been known to damage the drivetrain and they will be responsible for it. That usually does the trick. In any case, even doing the idle test requires that my cats be heated up.

On one occasion, I failed emissions, changed the oil and then passed with a significantly better reading. So I always plan to test right after an oil change. I even run a bottle of GTP prior just for good measure, but be sure to do that before you change the oil so whatever crud is cleaned from the engine with GTP isn't sitting in the oil pan.

https://www.amazon.com/CRC-05063-Guaranteed-Emissions-Formula/dp/B000CIPUR8/

 

[natejgreene9871]

My experience has been 100% in line with @gsxr's post #5. The old catylitic converters don't really do a good job until really warmed up (probably the reason for the air pump). In order to get mine through emissions I drive it to the testing facility in second gear and 4000 RPM for a few miles prior and if I'm waiting in line I'll also bring the RPM up to 3000 for a few minutes just before my turn (just keep an eye on the coolant temp).

I don't know what state you're in but here in Arizona the 500E/400E from 1992-1995 is exempt from doing the dynamic roller test due to the ASR. Since you have ASR you should be exempt. Sometimes I have to request a supervisor to convince the testers. If push comes to shove I tell them that the roller test has been known to damage the drivetrain and they will be responsible for it. That usually does the trick. In any case, even doing the idle test requires that my cats be heated up.

On one occasion, I failed emissions, changed the oil and then passed with a significantly better reading. So I always plan to test right after an oil change. I even run a bottle of GTP prior just for good measure, but be sure to do that before you change the oil so whatever crud is cleaned from the engine with GTP isn't sitting in the oil pan.

https://www.amazon.com/CRC-05063-Guaranteed-Emissions-Formula/dp/B000CIPUR8/

View attachment 188397

What happens if you put an asr car on a roller test? I didn’t know that was a problem

 

[a777fan]

What happens if you put an asr car on a roller test? I didn’t know that was a problem

I don’t think its a problem in the sense that it causes damage to anything… but a lot of the old traction control systems involved ecus that would pull timing when they sense wheel slip. Pulling timing will mess with your emissions and invalidate the test.

Typically these roller tests are one axle setups. Depending on how the specific system works (for example if wheel spin is detected by comparing front and rear wheel speeds) this could result in the ECU detecting wheel spin and pulling timing.

Note- this has always been my theory, but I haven’t any data to back it up. Hopefully someone more knowledgeable and with actual experience can confirm or deny.

 

[Gbowman]

Read the end of post #5 above. Also, go for a longer test drive... 3 miles isn't getting anything near operating temp. 30 minutes would be a good exercise.

I ended up taking it for a longer test drive. The misfiring issue came back. I took the caps and rotors off again and found that I somehow missed that the drivers side cam seal was leaking. I put new seals, caps, and rotors on and it seems to be running better than ever.

I took it to emmisions again and it still fails. It just barely failed on NOX and was more than double over on HC's. Im begining to think it may be bad cats. I scoped them out and took a few pictures. They look dirty but they didn't look melted or anything like that.

Is there anything else I should check before dumping a bunch of money on cats that may or may not fix the issue?

 

[natejgreene9871]

I ended up taking it for a longer test drive. The misfiring issue came back. I took the caps and rotors off again and found that I somehow missed that the drivers side cam seal was leaking. I put new seals, caps, and rotors on and it seems to be running better than ever.

I took it to emmisions again and it still fails. It just barely failed on NOX and was more than double over on HC's. Im begining to think it may be bad cats. I scoped them out and took a few pictures. They look dirty but they didn't look melted or anything like that.

Is there anything else I should check before dumping a bunch of money on cats that may or may not fix the issue?

I don't hear of MB cats going bad often unless they break up inside. how many hours of spirited highway driving have you done on this car? Preferably with some kind of cat cleaner in the tank. Maybe try some laquer thinner

 

[gsxr]

I ended up taking it for a longer test drive. The misfiring issue came back. I took the caps and rotors off again and found that I somehow missed that the drivers side cam seal was leaking. I put new seals, caps, and rotors on and it seems to be running better than ever.

Cool! Glad you got that taken care of.

I took it to emmisions again and it still fails. It just barely failed on NOX and was more than double over on HC's. Im begining to think it may be bad cats. I scoped them out and took a few pictures. They look dirty but they didn't look melted or anything like that.

Is there anything else I should check before dumping a bunch of money on cats that may or may not fix the issue?

No way I would replace the factory cats until you have positively ruled out every other possibility first. Aftermarket cats are vastly inferior to the factory units, and the factory cats should still function OK if the honeycomb is intact as seen in your photos.

Again, the catalyst must be FULLY HOT to get decent HC measurements. Simply heating the cats properly can make a huge difference in HC readings. Read more info here.

Also, check what LH module (fuel injection computer) is installed. It needs to be correct for the 1992 400E. If it is, next step is to open it up and verify nobody installed a "performance" EPROM chip, which could cause problems with emissions. Also verify the EZL is correct for a 1992 400E. You won't be happy if you install new cats and have the same emissions failures... you'll be out a bunch of money, have inferior cats, and the same unsolved problem.

 

[gsxr]

Also, forgot to ask - has this car passed emissions recently under the prior ownership? If so, are there any records of the past emission test results (borderline, or passed with flying colors)? Any records of work done since the last emission test that could explain why it's now failing?

 

[Gbowman]

I don't hear of MB cats going bad often unless they break up inside. how many hours of spirited highway driving have you done on this car? Preferably with some kind of cat cleaner in the tank. Maybe try some laquer thinner

That could be worth doing. I'm not sure about other states but in Colorado they give you a free e test 10 days after the first one. I might just drive the wheels off of it for a week with a bunch of additives in it and try and again to see what happens.

Cool! Glad you got that taken care of.




No way I would replace the factory cats until you have positively ruled out every other possibility first. Aftermarket cats are vastly inferior to the factory units, and the factory cats should still function OK if the honeycomb is intact as seen in your photos.

Again, the catalyst must be FULLY HOT to get decent HC measurements. Simply heating the cats properly can make a huge difference in HC readings. Read more info here.

Also, check what LH module (fuel injection computer) is installed. It needs to be correct for the 1992 400E. If it is, next step is to open it up and verify nobody installed a "performance" EPROM chip, which could cause problems with emissions. Also verify the EZL is correct for a 1992 400E. You won't be happy if you install new cats and have the same emissions failures... you'll be out a bunch of money, have inferior cats, and the same unsolved problem.

I agree. I have taken out the LH module and and ezl module and looked at them. I didn't take them apart but they are the correct year and don't look to be tampered with.

I ran it around for about 10 minutes at 3,000 rpm before getting to the emmisions place and there was no line so I got straight on the Dyno.

The previous owner was lucky and lived in a non emmisions county. From what he told me it sounds like it was sitting in a field for quite some time before he bought it.

Do you think the O2 sensor could be an issue. I know some vehicles will throw a code as soon as they see a small fault with the O2 sensors and others won't unless the car is barely running. Is there any way to test the O2 sensor or is it just one of those things that's just worth replacing?

 

[a777fan]

Oh no! A scotty vid linked on the board! Has hell actually frozen over???

 

[gsxr]

If the O2 sensor is questionable, just replace it... they aren't expensive. Details here. Hopefully it's not seized in place. Required reading below:

Oxygen Sensor removal, best tool? | M119 Engine

Hi, Thanks to this thread I ordered a new Oxygen sensor from Amazon, Bosch 13429 for my 1994 E500 http://www.500eboard.com/forums/showthread.php?t=824 Got the car on my lift, found the sensor, and WTF? How do I remove this thing? I don't think a regular 22mm wrench will work. -...

www.500eboard.co

Oxygen sensor information | M119 Engine

The oxygen (O2) sensors on the 500E/E500 are supposed to be replaced every 60kmi (100k km). The car may run fine with an old O2 sensor, however fuel economy is probably lower than normal (see attached PDF files for more info). The EPC specifies three different sensors, for different model years...

www.500eboard.co

With the new sensor in place, reset fuel trim / adaptation by "clearing" the 1 blink on pin #4, then drive the car for a couple hundred miles to let it re-adapt with the new O2 sensor.

It would be difficult to tell if the existing O2 sensor is bad without viewing live data to look for anomalies. Wouldn't hurt to eyeball the existing sensor/cable and see if it looks ancient vs recent.

 

[Gbowman]

If the O2 sensor is questionable, just replace it... they aren't expensive. Details here. Hopefully it's not seized in place. Required reading below:

Oxygen Sensor removal, best tool? | M119 Engine

Hi, Thanks to this thread I ordered a new Oxygen sensor from Amazon, Bosch 13429 for my 1994 E500 http://www.500eboard.com/forums/showthread.php?t=824 Got the car on my lift, found the sensor, and WTF? How do I remove this thing? I don't think a regular 22mm wrench will work. -...

www.500eboard.co

Oxygen sensor information | M119 Engine

The oxygen (O2) sensors on the 500E/E500 are supposed to be replaced every 60kmi (100k km). The car may run fine with an old O2 sensor, however fuel economy is probably lower than normal (see attached PDF files for more info). The EPC specifies three different sensors, for different model years...

www.500eboard.co

With the new sensor in place, reset fuel trim / adaptation by "clearing" the 1 blink on pin #4, then drive the car for a couple hundred miles to let it re-adapt with the new O2 sensor.

It would be difficult to tell if the existing O2 sensor is bad without viewing live data to look for anomalies. Wouldn't hurt to eyeball the existing sensor/cable and see if it looks ancient vs recent.

Sounds like a good plan. I already found out that the O2 sensor is properly seized in there when I went to scope the cats.
Wouldn't budge with an O2 socket and PB blaster. Ended up drilling small holes in the exhaust and welding them back up to look at the cats.

Guess I'm gonna spend the weekend trying to get that thing outta there.

 

[natejgreene9871]

Oh no! A scotty vid linked on the board! Has hell actually frozen over???

Yes haha

 

[natejgreene9871]

After cleaning under your cap you said it is “running better than ever”.

How much better?

Your engine should be smooth as glass when it is running properly. When I am sitting at a stoplight I usually can’t feel that it is running.
How does your car compare to this statement?

Are you sure you don’t still have a misfire? Based on what I have read a misfire will cause high HC

See here:

https://www.reddit.com/r/MechanicAdvice/s/amZ7eURQBo

 

[Gbowman]

After cleaning under your cap you said it is “running better than ever”.

How much better?

Your engine should be smooth as glass when it is running properly. When I am sitting at a stoplight I usually can’t feel that it is running.
How does your car compare to this statement?

Are you sure you don’t still have a misfire? Based on what I have read a misfire will cause high HC

See here:

https://www.reddit.com/r/MechanicAdvice/s/amZ7eURQBo

Funny I was reading that same reddit thread earlier today.
It seems to me like it is running perfectly fine. No occasional misses or dead miss or anything of the sort.

 

[gsxr]

On the odd chance it's unburned fuel... is the fuel pressure regulator good? Right after shutdown, remove the vacuum hose, there should be zero evidence of fuel at the vacuum port.

Per the Reddit thread smog tech, it would be a good idea to open up your LH module and make sure someone didn't install a "performance" EPROM that could be messing things up. There was a tool on eBay that for many years sold 5.0L EPROM's for 4.2L engines, which could cause emissions test failures. If something like this is going on, no amount of ammunition loaded into the parts cannon will help.

Other internet sources mumble about high HC with high NOx possibly indicating a lean condition. Have you performed a smoke test to check for intake leaks?

Does the engine pull strongly to redline (6000rpm) at WOT? I'm curious if the cats could be partly blocked but this is difficult to confirm without measuring backpressure, or if there's a loss of power at high RPM... but with a "new" car you may not know what normal power is at high RPM.

Finally. Can you post the most recent emissions test data?